Summary
A high-level summary is presented here in quick, bulleted form. More details are provided below.
- For highest reliability, fastest/easiest "out of the box" operation, and backup mailbox functionality, use an external, full-function, hardware TNC
- Use high-quality, shielded cables, with ferrite beads
- Adjust your TNC for optimal deviation, depending on the audio output of each radio
Details
Hardware TNCs
- Full-function hardware TNCs, which implement the full AX.25 protocol stack, are the easiest to use and most reliable option, especially for EmComm work.
- Indicator lights on the front are useful for troubleshooting.
- Command mode options allow complete customization of the operation of the TNC.
- The internal mailbox can be used in a standalone configuration to receive messages "when all else fails".
- Some TNCs allow deviation to be set with a software command making it easy to switch between radios.
- Some TNCs include on-board help, which reduces the need to keep a user manual nearby.
- KISS-mode hardware TNCs are not full-function TNCs. KISS (Keep It Simple, Stupid) mode simply converts between digital signals (the AX.25 1s and 0s on the serial cable) and audio signals (used by the radio). But it doesn't understand what's in the AX.25 packets. KISS-mode TNCs require the use of additional software to perform the AX.25 protocol functions. Many users report difficulty and some bugs when using this extra software.
- Integrated TNCs are hardware TNCs integrated into the radio. They are convenient because there is one less physical device and one less cable to carry and connect. But they are also a single point of failure. If the internal TNC dies, you can attach an external TNC. But if the radio dies, you typically need another radio and another TNC. Most integrated TNCs do not have the full feature set of standalone TNCs. For example, most do not have a private mailbox function. Some will not operate with open squelch, which is not very important for a field user station, but is more important for an unattended BBS location.
Software TNCs
- So called "software" or "soundcard" TNCs use the PCs internal sound card or an extra, add-on sound card to produce the outbound audio going to the radio and decode the inbound audio coming from the radio.
- These "software" TNCs require the use of additional software to perform the AX.25 protocol functions. Many users report difficulty when using this extra software and there are known and unfixed bugs.
- An external soundcard (usually connected with USB) can avoid most problems with PC operating system sounds going to the radio or with different applications adjusting the audio levels. USB can be susceptible to RF interference, so keep the cable coiled up short and use ferrite beads. Still, many users report difficulty with the software and there are known and unfixed bugs.
- If a soundcard TNC is all that is available, then it's better than nothing. But it is not recommended for EmComm, where the station needs to simply plug in and work, each and every time, with minimal configuration.
Cables
- TNC-to-Computer
- Serial
- The TNC-to-computer cable is an RS-232, straight-through cable. The most common configuration is a DB-25 male (at the TNC end) to a DB-9 female (at the PC end). Some TNCs use a different connector.
- If your computer does not have an RS-232 connection, use a USB-to-serial adapter.
- USB
- Newer TNCs may have a USB connection. But often this is simply a built-in USB-to-serial adapter; the computer will still see a serial interface.
- Even if you decide to purchase a TNC with a USB interface, it is wise to keep a USB-to-serial adapter in your go kit, just in case you need to connect to a different TNC or some other device with a serial interface.
- TNC-to-Radio
- The TNC-to-radio cable carries audio, squelch and PTT signals and is specific to the particular TNC/radio combination. Many Kenwood and Yaesu mobile radios use a 6-pin mini-DIN connector with a common pin-out. The Alinco radios use a DB-9 connector.
- Consult the TNC and radio manuals for the proper pinouts on each end of the cable.
- The SCCo BBS sites and SCCo EOC and many individuals use cables built by Associated Radio (www.associatedradio.com).
- Ferrite beads
- Any cable will act as an antenna and the common-mode currents induced by the received RF signal can create strange behaviors in PCs and other data devices. This is especially true in field stations, where the antenna may be near the data devices. Coil up excess cable to reduce its effectiveness as an antenna and place ferrite beads at each end of the cable to further impede common-mode current flow.
Notes on Specific TNC Configurations
- The SCCo BBS sites, the SCCo EOC, the SCCo ARES/RACES communications trailer, the SCCo Interoperability trailer, and most city EOCs use the Kantronics KPC-3+ TNC. It has several advantages:
- It has indicator LEDs on the front which are useful for troubleshooting
- It has a command mode and implements the AX.25 protocol so it can be used directly with Outpost without the need for additional software
- FM Deviation level can be set with a software command. Once you know the proper setting for each radio, you can easily switch between radios without the need for hardware adjustments or test equipment.
- It has an internal mailbox that can be used "when all else fails".
- It has on-board help for each command, reducing the need to have a user manual.
- It operates on a wide input voltage range (it can run on 9V or 12V batteries), and draws less power than many other TNCs.
- Newer models have a USB interface. But note that this USB interface is simply a built-in USB-to-serial adapter. The PC will still see a serial interface.
- The Timewave PK-96 is used at some SCCo BBS sites.
- It does not include on-board help
- The deviation must be set with a potentiometer on the back while observing a service monitor or deviation meter. This makes it less desireable as an end-user TNC because it's more difficult to switch between radios that require different audio levels.
- It does perform well at 9600 baud, The SCCo network does not currently use 9600 baud. But it might be an option in the future.
- It does perform well for BBS forwarding (BBS-to-BBS communications). There is a well-known problem with the Kantronics KPC-3+ that will cause it to become hung when operating in KISS mode on a BBS forwarding interface. So, we use the PK-96 on our BBS-to-BBS forwarding interface.
- The SCCo application note "TNC Standard Parameter Settings" contains detailed configuration information about the most common TNCs in use throughout the county. It covers in detail the TNCs that are supported by preconfigured settings files in the SCCo installer version of Outpost. It also contains notes about compatibility with other TNCs that have been seen over the years of operation of the SCCo packet network.
- The SCCo BBS sites, the SCCo EOC and several other sites use TNC-to-radio cables from Associated Radio (http://www.associatedradio.com/nkeyword_srch.php?keyword=tnc+cable&submit=Search).
Questions / Comments
The SCCo Packet Operations training classes cover the above information and much more. Consult the training course materials for more detail.
If you have a question about any of the above information, someone else probably does, too. So post your question to our packet discussion group where all of our local users can see the question and the answer.
This page was last updated on 08-Mar-2020